This invention relates generally to cameras and more particularly concerns apparatus for indicating the advancement of film in cameras.
In some areas of camera use, such as in scientific research, it is desirable to have a highly reliable photographic system. In the Space Shuttle Program, one such area, the external cameras of the Shuttle are subject to the extreme cold of space. In extreme cold, the film becomes brittle and needs to be monitored for breakage. A mechanism that will accurately monitor film advancement in the remote Shuttle cameras and provide a positive indication of proper advancement is needed.
Previous mechanisms have not proven to be entirely satisfactory. For example, one such mechanism has a sensing finger that by detecting the presence of perforations in the film, usually one per frame, can tell whether the film is advancing. This sensing finger actually enters the perforation and prevents further advancement until it is withdrawn. Inherently this type of mechanism damages film and impairs camera operation. In the Shuttle Program it is important that the mechanism in no way damages the film or impairs the operation of the camera.
Another mechanism indicates film advancement by detecting when film is delivered from a film roll. A cam-like block is mounted on the shaft supporting the film roll so that the block rotates when the shaft rotates. When the block rotates, the corners of the block touch a flat strip located parallel to the periphery of the block causing the strip to lose contact with an electrical circuit. This intermittent loss of contact with the circuit causes a light to flash, indicating that film has been delivered from the roll. This type of mechanism inherently involves wear, thus reducing its reliability.
Since the cameras now in use are very reliable, a simple add-on mechanism to indicate proper film advancement is desired. Previous mechanisms have not been satisfactory in that they reduce the reliability of the camera.
Accordingly, an object of the present invention is to detect film advancement without damage to the film or impairment of camera operation.
Another object is to indicate whether the film is advancing properly frame by frame without use of special film.
A further object is to detect film advancement in remote cameras and provide a positive indication of proper advancement.
Still another object is to provide an indicator that can be added to the camera without affecting its photographic or operational reliability and without major modifications.
Other objects and advantages of this invention will become apparent hereinafter in the specification and drawings.